Fears are rising that Sudan's 2005 comprehensive peace agreement (CPA) which ended decades of north-south conflict is about to collapse as it approaches its biggest test – a nationwide referendum on southern independence scheduled for 9 January.

This intensification of international misgivings was predictable. The ruling National Congress party was never going to accept southern secession without a fuss; after all, what government would blithely accede to the partition of its sovereign territory?

Ongoing disputes about borders, oil revenues, the Abyei region, and voting reflect long-standing mutual mistrust, tribal enmities and the organisational limitations of a vast, under-developed, relatively poor country. All this is raising the temperature.

But a less obvious reason why the alarm bells are ringing is the growing tendency among Washington politicians and pressure groups to divide the rival Sudanese leaderships into "good guys" and "bad guys", into freedom fighters and evil-doers.

Five years ago the US and other interested parties decided a peace deal was more important that apportioning blame for the war or, for example, the crisis in Darfur. This pragmatic impartiality is now dissipating.

Northern Sudanese officials and diplomats are convinced the Obama administration in particular, and the west in general (including the UN), is rooting, Kosovo-style, for southern independence, the referendum's expected outcome.

Salva Kiir, the Sudan People's Liberation Movement (SPLM) chief and southern president, is a persuasive advocate, as he showed again last week during a visit to Juba by UN security council envoys. His smooth political skills contrast sharply with the tough-guy style of Sudan's president, Omar al-Bashir.

Kiir seems to have become a favourite of Susan Rice, the US ambassador to the UN, and her boss, secretary of state Hillary Clinton. Both are highly critical of Bashir. On her return from Sudan, Rice repeated Kiir's warning "the north may be preparing for war and may be moving troops southwards" – an assertion for which she offered no evidence and which is strongly denied in Khartoum.

Rice's proposal for border buffer zones has now been adopted and has received a dusty response. The decision "reflects nothing but ignorance of the facts on the course of events in Sudan or harassment aimed at [Sudan's] stability and integrity", a Sudan army spokesman said. He implied the expanding UN troop presence could increase rather than reduce tensions ahead of the vote.

US pressure groups backed by the Christian right purposefully pursue the demonisation of Bashir's government. Having failed to gain his arrest on Darfur-related charges of genocide and war crimes, charges that Khartoum, the African Union and the Organisation of the Islamic Conference flatly reject, activist groups such as the Enough Project are accusing Bashir of planning another bloodbath. They even suggest direct US military intervention may be necessary.

"If we do nothing, if we turn our backs and walk away, 100,000 people, half a million people, a million people are going to die," the actor George Clooney, a prominent Enough supporter, claimed last week. Pressure groups have lobbied hard against efforts by some Obama administration officials to engage more constructively with Khartoum. And renewed north-south conflict would undoubtedly bring fresh calls for the US to step in.

Abdullahi al-Azreg, Sudan's ambassador to London, dismissed predictions of looming mayhem as insulting and exaggerated but admitted there were serious problems. Kiir had broken the south's word over the CPA, by pressing for independence rather than trying to make unity "attractive", as Juba undertook to do, he said.

"The SPLM is ruling the south through the barrel of a gun. It is intimidating the voters," he said. "The last election [in the south in April] was not fair, it was not transparent, it was rigged. If the referendum is the same, we could not accept it, we would reject it. If there was fraud, we would say so straight."

But Azreg was adamant the north would not resort to violence if the south voted for independence. "We will not use violent means to stop it. We don't want war." Secession would amount to an "earthquake" affecting not just Sudan but also neighbouring countries, some of which would try to exploit it, he said. An impoverished, under-populated, newly independent south would face a rough ride. But suggestions that Khartoum would oppose it with force were ignorant or malicious or both.

"Sudan has become an issue in internal US politics. They constantly distort our image. They depict us as demons. It is part of the general atmosphere of Islamophobia. How do I persuade you we are not demons?"